Recently, development related to self-driving automation for motor vehicles has been advanced. Automation levels defined by National Highway Traffic Safety Administration (NHTSA) in 2013 are classified into no automation (level 0), function-specific automation (level 1), combined function automation (level 2), limited self-driving automation (level 3), and full self-driving automation (level 4). The level 1 is a driving assistance system automatically performing one or more of acceleration, deceleration, and steering individually, and the level 2 is a driving assistance system automatically performing two or more of acceleration, deceleration, and steering in unison. In either case, driver intervention for a driving operation is required.
The automation level 4 is a full self-driving automation system automatically performing all of acceleration, deceleration, and steering, and the driver does not intervene the driving operation. The automation level 3 is a limited self-driving automation system automatically performing all of acceleration, deceleration, and steering, but the driver performs a driving operation according to need. The automation level changes according to a road environment. For example, during driving at the automation level 2, when a vehicle enters a section where a compartment line indicating a lane is faint, steering cannot be controlled in the vehicle. Then, the automation level immediately shifts to the automation level 1 in which only acceleration or deceleration for following a leading vehicle with a constant following-distance being kept is controlled. For example, when a self-driving specific lane ends 500 m away during driving at the automation level 3, the control of acceleration, deceleration, and steering is terminated. Since the automation level then shifts to the automation level 0, the vehicle requests a driver earlier to restart driving with a sufficient time allowance, and in response to the request, the driver drives the vehicle. As a result, the automation level shifts to the automation level 0. The shift of the automation level to a lower level when the vehicle is driven at the automation level 2 is called mode switching such that the self-driving mode in which the vehicle controls automatic driving is switched into a manual driving mode in which a driver performs a part or an entire part of a driving operation. Hereinafter, states of the automation level 2 and higher automation levels before mode switching are called a self-driving mode. A state in which the automation level is lower than before the mode switching after the mode switching is called a manual driving mode. As a method for switching the self-driving mode into the manual driving mode, there have been proposed a switching method using a switch or a panel operation, a method with which a driver directly operates an accelerator pedal, a brake pedal, and steering (overriding), and a method for detecting a state of a driving operation and switching a driving mode (for example, see PTL 1).